1. Field of the Invention
This invention relates to the detection of fluid leaks and to a determination of the rate of fluid leakage from various and individual leak sites. More particularly, the present invention relates to a method and apparatus for detecting and determining the rate of flow of fluid leaks in a piping system having a variety of different piping system components.
2. Description of the Related Art
In industrial piping systems, fluid leaks are one of the main causes of system inefficiencies, resulting in wasted energy costs, environmental hazards, and increased manufacturing costs. Most distribution systems have been estimated to waste about 10-20% of their capacity to leakage, and it is not uncommon in large piping systems to have from 200-500 or more fluid leaks occurring simultaneously. The accumulative effects of these leaks can result in losses of hundreds of thousands of dollars per year and can result in needless capital expenditures for new or additional equipment installed to offset the effects of the leakage.
Past efforts to locate and quantify these leaks for repair scheduling have not been very successful. For example, industries formerly would take annual or bi-annual plantwide "cold shutdowns" in order to make repairs or add new equipment. When the system was ready to be started up again, there would be a small period of time when leaks could be detected and repaired. This occurred because the fluid distribution systems were often one of the first systems brought back on line after shutdown and, while the other systems were not yet running, many leaks could be audibly located. However, this brief time period was often not enough to perform all the necessary repairs and generally only the large leaks were repaired if time allowed.
More recently, industry has adapted to obviate the need for complete shutdowns for repair and modification of equipment by taking more frequent but smaller sectional shutdowns, called "partial outages." While this allows the facility to continue operation and avoid start up expenses, it hinders even more the ability to accurately locate and quantify leaks because the leaks are more difficult to hear with part of the system running. This, in turn, hinders the ability to strategically plan partial shutdowns for leak repair while also making cost and environmental effect estimates difficult.
Nevertheless, because the leakage at most fluid leak sites emits sounds having components in the ultrasonic frequency range, an ultrasonic sound detector, as described, for example, in U.S. Patent No. Re. 33,977, can provide an instrument to locate a leak site. The use of such an ultrasonic sound detector does not require facility shutdown, thus allowing for "on the run" leak detection.
However, one of the main problems with current ultrasonic leak detection methods is the inability to accurately compute the size and flow rate of a given leak once it has been detected. Some leak flow quantification methods only categorize the leak flow rate as "small", "medium", or "large". Others, such as that disclosed in U.S. Pat. No. 5,136,876, for example, determine an approximate leak flow rate by comparing the measured sound pressure level with a standard curve that plots gas leak rates versus sound pressure level without respect to the nature of the leak site. The inaccuracies resulting from such methods are generally due to failure to deal with variations in the size of the leak site, the influence of the configuration of the fluid system element at the leak site, variations in the properties associated with the type of fluid which is leaking, and variations in the system temperature and pressure of the fluid. Additionally, the qualitative "small-medium-large" categorization is wholly inadequate for determining dollar amount lost per year, possible environmental damage, and system maintenance and repair requirements.
It is thus one object of the present invention to provide a more accurate method for quantifying leak flow rates.
It is another object of the present invention to provide a more accurate method for detecting leak flow rates which can accurately estimate the yearly cost and volume loss of one individual leak or a system of leaks.
It is yet another object of the present invention to provide a method for creating a database which provides a more accurate representation of the rate of flow of fluid leaks.
It is another object of the present invention to provide a mobile apparatus which can more accurately determine leak flow rates.